A health worker inspects an open vial of oral polio vaccine during a pulse polio round. On the Vaccine Vial Monitor (VVM) attached to the vial, the inner square is still lighter than the outer circle. What action should be taken?
- A Use the vial, as the vaccine is potent ✓
- B Discard the vial immediately
- C Return the vial to the district store for retesting
- D Dilute the vaccine before use
Correct answer: A. Use the vial, as the vaccine is potent
Explanation
On a VVM, the inner square being lighter than the outer circle means cumulative heat exposure has not yet reached the discard point and the vaccine remains usable. The vial should be discarded when the inner square matches or becomes darker than the outer circle, indicating heat damage. VVMs read heat exposure, not potency loss from freezing, and there is no field procedure for retesting or diluting a vial based on its monitor.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.